Prebiotics are the types of fibre in our food that feed our gut bacteria.
Find out about the different types of prebiotic.
Are prebiotics carbohydrates? What is the difference between simple & complex carbohydrates?
What foods contain prebiotics?
What is dietary fibre or roughage?
Find out about insoluble & soluble dietary fibre.
Are Prebiotics Carbohydrates?
Most of the foods we eat are forms of carbohydrates.
Carbohydrates are chains of sugar molecules.
Most carbohydrates are easily broken down into sugar molecules when eaten, giving us an instant energy boost.
Prebiotics are the types of carbohydrates that feed our gut bacteria.
They are the types of carbohydrate that our bodies can’t break down into sugar molecules.
This type of indigestible carbohydrate is called complex carbohydrates, or fibre.
What’s the difference between simple & complex carbohydrates?
Simple Carbohydrates are not prebiotics.
Starches (like pasta, white bread, white rice) are formed of short chains of sugar molecules.
These are broken down by our body’s own enzymes in the stomach & small intestine.
They are absorbed straight into the bloodstream giving a burst of energy.
Simple carbohydrates don’t reach our gut bacteria in the large intestine, so are not prebiotics.
Are longer chains of sugar molecules, which are harder to break down.
These pass undigested from the small intestine into the colon (large intestine), without releasing sugar straight into the bloodstream.
Here our gut bacteria ferment them and break them down into energy, nutrients & useful chemicals.
These types of carbohydrates are known as polysaccharides (poly = many, saccharides = sugars), dietary fibre or complex carbohydrates.
They are the long chains of sugar molecules found in plants, giving structure & acting as energy stores within the plant.
The Different Types of Prebiotic:-
There are thousands of different types of complex carbohydrates that feed our gut bacteria in fruit & vegetables, beans & wholegrains.
– Pectin, (found in fruit)
– Inulin (found in onions, leeks, garlic & other foods)
– Fructo-oligosaccharides or FOS (found in beans, wholegrains and many types of fruit & vegetables)
Prebiotic fibres or complex carbohydrates are also found in human breast milk.
– Called Galacto-oligosaccharides or GOS for short, these are long chains of sugar found in breast milk.
Resistant starch is another type of prebiotic.
It’s a complex carbohydrate that forms when potatoes or rice are cooked and then cooled, which changes the sugars into longer chains.
These long chains pass undigested to the large intestine, where gut bacteria break them down.
Potato Salad (cold, cooked potatoes) and Sushi Rice (cooked, cooled rice) are examples of foods that contain resistant starch.
Bacteria also eat food sheltered within the tough outer coatings of unrefined and unprocessed wholegrains.
These coatings can be too large for our body to breakdown in the stomach and small intestine, so pass undigested to the colon.
For example, a whole oat has a protective outer coating, which allows the oat inside to survive the journey to the colon mostly intact.
Bacteria can then break down both the coating and the inside of the oat.
Quick cook / rolled oats have had the protective coating on the oat removed.
This means the simple carbohydrates inside can be easily digested in the small intestine.
Our body can easily break them down into sugar molecules and absorb them straight into our bloodstream.
Not all fibre is prebiotic
Some fibres, like cellulose (a tough woody fibre that gives structure to plant cell walls), can’t be broken down by our gut bacteria and it passes out undigested.
Dietary Fibre : Insoluble & Soluble
Dietary fibre is the non digestible fibre from the plant foods we eat.
It’s also known as roughage or complex carbohydrates.
You might have heard of fibre described as either insoluble or soluble.
Plant foods (vegetables & fruits, grains and beans) contain both of these types of fibre, the quantity varies by plant.
Soluble fibre dissolves in water, and is broken down by gut bacteria.
Insoluble fibre doesn’t dissolve in water.
– Some types of insoluble fibre can’t be broken down by gut bacteria (like cellulose) and passes through undigested, helping to bulk up stools.
– Other types of insoluble fibre are prebiotics (like resistant starch) and can be fermented (broken down) by our gut bacteria.
Some types of prebiotics are soluble dietary fibre, other types are insoluble dietary fibre.
Eat a variety of types of prebiotics for helpful gut bacteria
Eating a wide range of foods containing prebiotic fibre or complex carbohydrates will help a wide range of gut bacteria thrive in your large intestine.
Different types of bacteria feed on different types of prebiotic, so eating a varied mix of prebiotics is key for a diverse microbiome.
The Science Bit
The information I share on this site distills the research I’ve read on the microbiome, prebiotics & probiotics.
You’ll find links to the relevant research studies on each page.
I’m not a scientist / dietician / nutritionist. I’m a food lover & home cook, putting microbiome research findings into action in my kitchen.
Find out more about the scientists leading research into the microbiome on the FAQs page.